Pneumatic feed regulating mechanism



PMSMATTC FEED REGULATING M 1928 4 Sheets-Sheet l Filed Dec.

4 Sheets-Sheet 2 E@ wm am wm Q Lw Imfen'ns al/'dsoz C22' S Dec. 9, 1930. P. DAVIDSON ET AL PNEUMATIC FEED REGULATING MECHANISM 4 Sheets-Sheet 5 ALIA Dec. 9, 1930. P. DAvlDsoN ETAL PNEUMATIC FEED REGULATING MECHANISI Filed Dec. 22, 1928 (n I j! l ,I fd i! Il iff 121/ @n l i f5 W95 ,il Il ,2f 51 A93/ wg; l7,/ y b 4M E: J9 f @gg/H J6 iff/5% 21941 62 Y l 15%@ ,n l 3% f f?. f f 1g; 55 l g 1/[7 5% Ll if@ f5? 165 3m mm Dec. 9, 1930. P. DAVIDSON ETAL 1,784,483

PNEUMATIC FEED REGULTING HECHANISK Filed Dec. 22, 1928 4 Shasta-$11691'I 4 Patented Dec. 9, 1930 UNITED STATES PATENT OFFICE PHILI? DAVIDSON, OF NEW YORK, N. Y., AND JO CRITES, OF EVANSTON, ILLINOIS,

ASSIGNORS T0 INTERNATIONAL COMBUSTIION ENGINEERING CORPORATION, OF NE YORK. N. Y.,A CORPORATION OF DELAWARE PNEUMATIC FEED REGULATING MECHANISM Application led December 22, 1928. Serial Nc. 327,916.

This invention relates to a feed regulating mechanism for pulverizing or grinding mills, and more particularly a pneumatically actuated means for automatically regulating the 5 speed of the variable speed motor which drives the feed regulating mechanism.

Pulveiizing or grinding mills of the sype to which this invention is applied utilize an air lift separation process, produced by a suction fan or similar means, whereby t-lie material that has reached the proper degree of pulverization is withdrawn in suspension in air. Ordinarily in a mill of this type air'is introduced into the mill below the region in which the material is pulverized and consequently, if the mill becomes overloaded because the material to be pulverized is fed in at a greater rate than the pulverizcd material is withdrawn therefrom, the air inlets will become somewhat clogged and the vacuum in the upper part of the mill and in the pipe leading therefrom to the fan will become intensified. The present invention vrelates to a mechanism for regulating the introduction of the material into the mill in response to fluctuations in the vacuum maintained in the mill` whereby in case the mill becomes overloaded or tends to become overloaded the feed will be interrupted or diminished in quantity.

rlhe general objectof this invention is to provide a pneumatically actuated means, responsive to the degree of vacuum in the mill,

.1 .tor automatically .controlling the speed of the motor which drives the feeding mechanism.

Another object is to provide pneumatically actuated means for successively actuating a series of switches whereby the speed of the motor is controlled.

Numerous ether objects and advantages of this invention will be more apparent from the foliowin; r detailed description of one appi-m'r-l iormuof apparatus adapted to carry out the principles oi' this invention.

ln the `accompanying drawings:

Fig. a side. elevation, partially in section. mf' :a pulveriziug mill with the apparatus of the sent invention applied thereto.

Fi.;l s a detail vertical section. on a larger scale, through the intake ends of the suction central vertical axis of the mill.

and pressure conduits leading to the pneumatic control mechanism. I f Fig. 3 is a front elevation, artially in vertical section, of the assemble pneumatically controlled switches. l

Fig. 4 is a vertical section, taken substantially on the line 4.-'4 of Fig. v3.

Fig. 5 is a central vertical section through one of the pneumatic control valve tnechanisms, the view being taken substantially on the line 5 5 of Fig. 3. In order to simplify the disclosure, the two horizontally extending pipe connections of Fig. 3 have been illustrated in positions at from theiractual position in Fig. 5. Since the structure is otherwise symmetrical about the central axis of the valve mechanisms, this change does not otherwise aiect the accuracy of the drawings.

Fig. 6 is a vertical central section throu one of the suction motor devices and t e switch actuated thereby. This view is taken substantially on the line 6-6 of Fig. 3.

Fig. 7 is a wiring diagram illustrating the operation of this mechanism in connection vith a typical motor speed control installa- Referring first to Figs. 1 and 2 of the drawings, 1 indicates the casing of a pulverizing mill of the Raymondwtypg the pulverized material being withdrawn Ain suspension in air through the pipe 2 by lmeans of the lsuction fan 3, or some equivalent exhausting mechanism. At 4 is indicated the bull-ring of the mill against which bear a series of rollers 5 :rotatably supported on pendant journals 6 which revolve around the Air is admitted to the mill through a series of inlets 7 located below the region in which pulveriztion takes place.

Material to he pulverized passes downwardly from a bin 8 through a chute 9, which terminates in a casing l0, in which is posi.- tioned a rotary pocket feeder of well known type. This feeder is driven at a. slow speed through suitable reduction gearing not here illustrated, but indicated generally at- 11, and belt gearing 12 from an electric motor 13. This motor 13 is of a variable speed type,

and provided with suitable speed control mechanism whereby its speed may be diminished or the motor may be entirely stop d, in order to regulate the rate at whic material is fed from chute 9 into the mill housing by means of the rotary pocket feeder. The object of this invention is to provide a mechanism for pneumatically controlling the speed of motor 13 in accordance with variations in the vacuum maintained in the upper portion of the mill housing and discharge pipe 2. There will always be a certain degree of vacuum maintained in the discharge pipe 2 by means of the exhausting mechanism 3 when the mill is in operation.

. If the mill becomes over-loaded through excess of materials fed into the mill over that discharged b the exhausting apparatus, the vacuum in tlie part of the mill above the region of pulverization will increase in intensity, due to the increased resistance of the accumulated solids in the mill to the entrance of air throu h the openings 7 beneath the pulverizing rollers 5.

A pressure pipe or conduit 14 and a suction conduit 15 both communicate with a manifold 16 mounted on and projecting into the upper portion of the mill discharge pipe 2. The lower ortion` of manifold 16- is curved at 17 in t e direction of travel of the pulverized material through pipe 2, so as to prevent the entrance of this material into the pressure and suction pipes. Suction pipe 15 communicates directly at 18 with the upper portion of the manifold casing so that the suction created in the discharge pipe 2 ma be communicated throu h manifold 16 an suction conduit 15 and its ranches (hereinafter described) to operate the several suction motor devices, whereby the switches are opened and closed. The pressure conduit 14 has an extension 19 projecting centrally throu h manifold 16 to a point near its inlet end w ereby the pressure (sub-atmos heric) existing in the discharge pipe 2 an upper portion of the mill will be communicated to the pneumatic controlling mechanism hereinafter described.

Referring now more particularly to Figs. 3 to 6 inclusive, a closed casin 20 positioned at any convenient location is adapted to house the pluralit of pneumatically actuated and controlla switches which form the particular subject matter of this invention. This casing 2O is entirel closed at its front, back, top and ends, an a horizontal partition 21 adjacent the bottom of the casing completes the closed chamber 22 in which the pneumatically operated devices hereinafter described are housed. Below the partition 21, the lower portion of casing 20 is divided by vertical partitions 23 into a plurality of air intake chambers 24. An air conduit 25 leads from each chamber 24 to one of the pneumatically controlled valves hereinafter described. The bottom of each intake chainber 24 is formed by spaced apart upper and lower perforated plates 26 and 27, between which is confined a mass of steel wool, or equivalent material 28. The two perforated bottom walls with the interposed loose mate` rial will admit air at atmospheric pressure to the housing and thence through conduits 25 to the pneumatic devices which' are mounted therein, but will serve to clean this air and prevent dust, owdered coal or other impurities from finding access to the pneumatic controlling devices. The front wall of chamber 22 may be in the form of/a glass plate 29, whereby the condition and operation of the mechanism housed therein may be observed at any time.

The motor controlling mechanism housed within casing 20 comprises a plurality (here shown as 3) of similar switches A, B and C which are adapted to be separately and successively opened or closed in accordance with pressure changes in the mill. The several switches A, B and C, as well as the pneumatic devices for separately actuating and controlling each switch, are substantial duplicates of one another. The parts of switch A and its accompanying pneumatic mechanism will be indicated by unprimed reference characters, and similar parts of the switches B and C and their coo erating pneumatic devices will be indicated y similar reference characters with the exponents a and b respectively.

Each switch A, B and C is mounted on and actuated by a pneumatically operated device, here designated as a suction motor, the casing of which is indicated at 30, and supported by legs or brackets 31 from the rear wall of housing 20. A closed suction chamber 32 is formed in casing 30, the front wall of this chamber being in the form of a flexible diaphragm 33. This diaphragm is subject on its outer side to atmospheric pressure, and on its inner side to the pressure of an expansion spring 34 conned between the diaphragm and the rear wall 35 of the housing, and to the pneumatic pressure maintained in chamber 32 through suction conduit 36 which communicates with chamber 32 through one side wall of the casing 30. This suction conduit 36 is provided with a suitable normally open cut-ofil valve 37, and forms substantially a continuation of a branch 38 of the suction conduit 15 leading from the mill, as will hereinafter be apparent. The several branches 38 of suction conduit 15 project downwardly through the top wall of casing 20. When the vacuum existin in the mill is placed in communication with chamber 32 through conduit 36, this chamber will be exhausted so that atmospheric pressure will force the diaphragm 33 inwardly. When this suction connection is cut off and atmospheric pressure is once lil more admitted toconduit 36, the spring 34 will return the flexible diaphragm 33 to its normal position, as indicated in Figs. 3 and 6.

A bellcrank lever 39 is fulcrumed at 40 between a pair of lugs 41 projecting from the upper portion of the cover plate 42 of the casing 30. The lon er downwardly projectin arm 43 of the ellcrank is pivoted at 44%)etween-a pair of lugs 45 projecting from a late 46 secured to the central portion of exible diaphragm 33.

The switch A is here shown as bein in the form of aclosed tube 47 containing a g obule of mercury 48 which will run from one end to the other of the tube as the tube is tilted either way from a horizontal position. The tube 47 is pivoted adjacent one end thereof at 49 on the suction motor casing. A ring or clamp 50 secured about an intermediate portion of tube 47 is ivotally connected with the lower hooke end 51 of a link 52, the upper threaded end 53 of which projects through an opening in the shorter horizontally extending arm 54 of bellcrank 39. Nuts 55 and 56 threaded on stem or link 52 permit the vertical adjustment of this link which supports the switch tube 47. By properly adjusting the nuts 55 and 56 the switch tube may be maintained in the properly tilted position when normal atmospheric pressure is applied to both sides of the flexible diaphragm 33. f

In the construction here shown all of the mercur tube switches A, B and C will have scribed. In the form of the invention here shown, the contacts 57 and 58 are placed in the right-hand end of switches A and B so that the circuits controlled by these switches will normally be open. On the contrary, the contacts 576 and 58b of switch C are located in the left-hand end of tube 47" so that the circuit controlled by this switch will normally be closed since the globule 48b of mercury will normally bridge the two contacts 57" and 58". It will be apparent that when any one of these switch tubes is tilted from its normal position so that the right-hand end is lowermost, the mercury globules will run to the opposite ends of the tubes and the circuits controlled by the switches will be made or broken as the case may be. While in the example here shown, switches A and B are normally open and switch C normally closed, it will be apparent as the description proceeds, that all three switches could be norma-ll closed or all three normally open, or any ot er combination of these normal positions, all depending on the t peof the motor control mechanism which tliese switches control.

The pneumatic controlling device 61 (shown in section in Fig. 5) is adapted, when a certain predetermined degree of vacuum or sub-atmospheric prelsure is reached in the mill, to place the suction conduits 36 and 38 in communication with one another whereby the suction motor 30 will be operative to tilt'the switch A and close the circuit controlled thereby. When a certain higher pressure has been reached in the mill, the connection betweensuction conduits 36 and 38 will be suddenly closed, and the suction motor 30 will be placed in communication with air at atmospheric pressure whereby the switch will be returned to its normal open position. The degree of vacuumv at which pneumatic controller 61 operates is adjustable, so that the three separate controllers 61,

61'L and 6l" may be set to separately and successively operate the three switches A, B and C at different sub-atmospheric fessure. The pneumatic controller 6l u in the present apparatus is substantially the same as the mechanism disclosed in the patent to Raymond 1,541,848, granted June 16,

1925. The controller comprises a casingV made up of casing sections 62, 63 and 64, a flexible diaphragm 65 being -clamped between casing sections 62 and `63, and a flexible diaphragm 66 being similarly clamped lbetween sections 63 and 64. The suction conduit 36 leading to the suction motor 30, above described, communicates with a chamber 67 formed by a web 68 within casing section 64. The branch suction conduit 38 leading from the mill communicates with a chamber 69 formed in the casing section 63 l by a web 70. This chamber 69 communicates bg an opening 71 in diaphragm 66 with the c amber 72 above the diaphragm. The diaphragm 66 is formed with another opening 73 whereby chamber 72 is in communication with a chamber 74 under said diaphragm.

A cap member 75 screwed onto the upstanding cylindrical portion'7 6 of ca sipg member 64 incloses a chamber 77 withmwhich communicates the conduit 25 whereby air at at- J mos heric pressure is admitted to the chamil ber 7. A duct or passage 78 formed in the wall of casing members 64`and 63 admits secured a plate 82 formed with a depending -of an adjusting screw 91 threaded into the cap portion of the spring-inclosing bonnet 92, the adjusting screw 91 being held in adjusted position by a lock-nut 93. A guide pin 94 for the lever 86 is secured at its lower end in casing 62 and projects upwardly through a slot 95 in the long arm of the lever.

A valve seat 96 is mounted in the lower web 97 of casing 63. An annular valve plate 98 adapted to close the passage 99 through valve seat 96 has a limited vertical movement in the annular recess 100 formed in the valve stem 101 which is secured by screw 102 to the upper face of the diaphragm plate 82. A

. spring 103 confined between valve plate 98 and a shoulder 104 at the upper end of stem 101 serves to normally hold the valve plate 98 at the lower end of '.he recess 100. A valve seat 105 is secured within the transverse web 106 of upper casing 64, and a movable valve plate 107 is adapted to alternatively close the valve opening through seat 105 or the opening through valve seat 108 formed in web 68, hereinabove referred to. The valve plate 107 is supported on flexible diaphragm 66 by valve stem 109 which is guided through the valve passages in webs 106 and 68. A central chamber 110 beneath diaphragm 66 communicates through a restricted passage 111 with the chamber 74 previously described.. For cleaning out possible accumulation of dirt in the restricted port 111. a screw plug 112 is provided in the side wall of casing 63 which has a semi-circular stud 113 projecting into the port lll.

The mechanism just described is shown in the drawings in the position taken when the vacuum in the mill is at or below normal. At this time communication is cut otil between the branch suction conduits 36 and 38 and the switch A will be in open position. rThe vacuum in chamber 8l is relativelyv low (or the pressure is relativelyhigh) so that the spring 88 through lever 86 holds the diaphragm 6.. in its upper position with valve 98 seated against valve scat 96. The low pressures dcvcloped in chambers 7;). and 110 b v means of the suction communicated through branch conduit 38 are equal since these chambcrs are in communication through the ports Til and 111. As a consequence. the atmospheric pressure in chamber 7T will hold the valve 10T down against valvil seat 108 thus cuttingr oil' communication between suction conduits- 38 and 36, and admitting air at atmo phcric pressure to the suction motor chamber 32 through conduit 25, chamber 77 valve passage in valve seat 105, chamber 67, and branch suction conduit 36.

Assuming now that the mill becomes overloaded through excess of material fed in over that discharged by the exhausting apparatus 3, the vacuum in the part of the mill above the region of pulverization will increase in intensity due to the increased resistance of the accumulated solids to the entrance of air through the inlets 7 below the pulverizing rollers 5. The lowered pressure in the mill will be communicated through conduits 14 and 80 to the chamber 81 of the controller 61 thus lowering the pressure below flexible diaphragm 65, and the atmospheric pressure communicated to chamber 79 above this diaphragm through passage 78 will push down this diaphragm against the adjustable pressure spring 88. The first downward Inovement of the diaphragm will not unseat valve 98 since the stem can slide for a certain distance through the valve compressing s ring 103. When however. the upper shoul er of the recess 100 on the valve stem comes against the valve 98, further downward movement of the diaphragm will unseat the valve and as soon as the air pressure is relieved on the under side of the valve 98 spring 103 will move the valve quickly against the shoulder at the lower side of the annular recess in the valve stem thus fully opening the port bev tween chamber 79 and chamber 110. Air at atmospheric pressure will instantly enter the chamber 110 from chamber 79, and since the port 111 through which chamber 110 communicates with chamber 72 is relatively small in comparison with the opening 71 leading from chamber T2 to the suction pipe 38, the pressure under diaphragm 66 will be greater than the pressure above the diaphragm so that valve 107 will be raised against its upper scat 105. thus shutting ofi' air at atmospheric pressure from the suction pipe 36 and placing this pipe in communication with the suction chamber Ti) and thence with suction Conduit 38. In other words. communication Will be established between branch. suction conduits 38 and 36 so that the suction in the mill will be communicated to suction motor chamber 32 to draw in thc flexible diaphragm 33, and through the lever and link connections tilt downwardly the right-hand end of mercurj.v tub" switch 4T .vliercupon mercury globnle 48 will roll to this end of the switch and complete the circuit between terminals .3T and This y'iositioning of thc various parts n ill persist as long as the abnormal vacuum in thc mill continues. As lsoon. bouwer, as

lun

tb- .uil has clearly rccstablished the normal vacunan therein. .spring 8S assisted b v the increased pressurc in chamber 8l will be able to rock lever 86 and push up the diaphragm 65 to again bring the valve 98 against its Vscat means 96 whereupon the pressures at opposite sides of diaphra 66 will again be equalized and the atmosp eric pressure on the upper side of valve 107 will again move this valve down against the valve seat 108 thus o ning the suction chamber 32 to the atmosp ere. The flexible diaphargm 33 of the suction motor will then be moved downwardly to a ain swing the mercury switch back to its initial position and break the circuit at contacts 57. t

- by cutting in or out the resistances 118 and and 58.

The constructionof this pneumatic controller 61 is such that the valve 107 will not be opened or closed in response to every slight and transitory fluctuation in the intensity of vacuum in the mill. The pneumatic device is actuated to move the valve at certain maximum and minimum degrees of vacuum in the mill, these limits being susceptible of adjustment by means of the adjusting screw 91 which controls the compression of spring88. The controller has a lag so that the maximum and minimum vacuums obtained must be of appreciable duration in order to bring about actuation of the control valve 107.

It will now be apparent that the adjusting screws 91 of the several pneumatic control devices 61 can be separately set so that the switches A, B and C will be successively actuated as different predetermined de of vacuum are attained in the mill. In the present construction, these devices are so adjusted that when no more thana normal deree of vacuum is established in the mill, that is when the rate of feed to the mill and the discharge of material therefrom is in satisfactory adjustment, all three of the pneumatically controlled units will remain 'in the noi-mal inoperative positions illustrated in the drawings. When a certain higher degree of yacuum is obtained in the mill, due to the partial clogging of the mill through overfeeding, the pneumatic device 61 operates to cause switch A to be tilted and close the circuit at contacts 57 and 58. When a Somewhat higher degree of vacuum is reached, the pneumatic device 61* will operate to tilt the switch B and close the circuit controlled by this switch. When a still higher degree of vacuum is reached, the pneumatic device 61" will o crate to tilt switch C and open the normally closed circuit controlled y this switch. As the vacuum in the mill is lowered, that is as the pressure is permitted to increase, the switch C, B and A will be returned to their normal positions in the order named, that is the switch A which was 0perated first will be the last to be returned to normal position.

In order to illustrate the actual operation of this mechanism in controlling the speed of the motor, a wiring diagram has been shown in Fig. 7, although it is to be understood that other electrical hook-ups could be used to control the speed of he motor. Re-

fering to Fig. 7, 114 and 115 are the two electric supply mains, and 116 indicates the manually operated switch b means of which the motor 13 is started. Mbtor 13 is of the shunt wound type, the shunt field being indicated at 117, and the resistances 118 and 119 bein in series with the shunt field and adjustab e b The speed o the motor 13 is adjustable by controlling the intensity of the shunt field 119. The resistance 118 is adapted to be cut outof the field circuit by means of the shunt circuit consisting of wires 121, 122, normally unconnected contacts 123 and 124, and wires 125 and 126.. A relay consisting of bridge plate .127 and actuating coil 128 is adapted to close the shunt circuit b connecting the contacts 123 and 124. In t e same manner a shunt circuit consisting of wires 126 and 129, spaced contacts 130 and 131, and wire 132, is ada ted to shunt the resistance 119 out of the geld circuit. The normally open contacts 130 and 131 are adapted to be bridged by the contact plate 133 actuated by the relay coil 134. The actuating circuit for relay 128 comprises wire 59, contacts 57 and 58 and mercury globule 48 of the switch A wire 60, coil 128, wire 135, wire 136, and switch 116 back to the negative main 1715. A similar actuating circuit for the relay 134 consists of wire 59", contacts 57' and 58* and mercury globule 48 of the switch B, wire 60, relay coil 134, wire 137, wire 186, and manually operated switch 116. Both of these relay circuits are normall open, since switches A and B are norma y open so that resistances 118 and 119 will norma y be in circuit with shunt eld 117, thereb weakening the field so that the motor w' operate at its maximum The armature circuit extends from positive main 114 through wire 138, contacts 139 and 140, starting resistance 141, the armature of 4motor 13, wire 142, series coil 143 of overload relay 144 wire 145, series coil 146 of the vibrating eld relay 147, and the wire 148 to the negative main 115. The line contacter relay 149, which is actuated by the coil 150, controls three movable bridge plates 151, 152 and 153 adapted to simultaneously control three separate circuits. The contact plate 151, when liftin from the normall open position shown 1n the drawings wil close the armature circuit through spaced contacts 139 and 140. The contact relay coil is actuated through a circuit consisting of wire 154, coil 150, wire 59", contacts 57" and 58" and mercury globule 48" of switch C, wire 60", spaced contacts 155 and 156 of the overload relay 144, wire 157, spaced contacts 158 and 159 of a control relay 160, and wire 161 and wire 136 to the manually operated switch 116. The coil 162 of control rela l 160 will normally be deenergized, and the the connecting section 120.

lli

contact plate 163 of this relay will bridge the contacts 158 and 159. Similarly the contact plate 164 of overload relay 144 will normally connect the contacts 155 and 156. The shunt coil 165 of overload relay 144 is connected with main 114 and lead wire 136 by means of wires 166 and 167, respectively. The energizing circuit for the coil 162 of control relay 160 is connected in series with the mercury switch A. The circuit runs from lead 60 of this switch through wire 168, contact 169, bridge plate 153, Contact 170, Wire 171, coil 162, wire 172 and wire 136 to the switch 116. Another shunt circuit around the field resistances 118 and 119 comprises the wires 173 and 174 and spaced contacts 175 and 176 which are adapted to be connected by the bridge contact plate 177 controlled by the vibrating field relay 147. The accelerating coil 178 for cutting out the startin resistance 141 is connected in a circuit inc uding the wire 179, spaced contacts 180 and 181, wire 182, coil 178, Wire 183, and negative main 115.

When the motor is to be started the operatox` closes the switch 116. At this time there is low suction in the mill since there is relatively little material in the mill and the air flow is not restricted. Consequently the mercury switches A, B and C will all be in their normal positions as indicated in the drawings. The previously traced circuit will be completed through closed switch C and the coil 150 of the line contact or relay 149 so as to move the bridge plate 151 into engagement with contacts 139 and 140, and the plate 152 into contact with spaced contacts 180 and 181. Simultaneously the bridge plate 153 will be moved out of contact with the fixed contacts 169 and 170. This will complete the circuit through the motor armature and the starting resistance 141, and at the same time the circuit through coil 178 will be completed to progressively cut out the starting resistance 141. However, since it is not desirable to start a motor with a weakened field, due to possible flashing at the commutator, the vibrating field relay 147 is introduced to short circuit the field regulating resistances. As the motor accelcrates. the relay vibrates to weaken the field gradually until the maximum speed of the motor occurs, and thereafter this relay remains open, as indicated in the drawings.

The motor 13 and the feeder actuated thereby are now operating at their maximum speeds. The suction in the mill will build up, and if the material is being fed too rapidly into the mill the vacuum in the mill will reach a sufficient intensity to cause the mercury switch A to be tilted thus closing the circuit at contacts 57 and 58 which actuates the relay 128 to complete the shunt circuit around field resistance 118. This will strengthen the field and cause the motor to slow down to an intermediate speed. If the vacuum in the mill continues to build up, mercury switch B will next be actuated to close the circuit through relay 134 thus closing the shunt circuit around the remaining field resistance 119, permitting field 117 to be energized to full strength and thus reducing the speed of motor 13 to its lowest operating speed. If, under these conditions, the motor speed is sufficiently low to enable the mill to clear itself, then the vacuum in the mill will be reduced and the switch B will open to dcenergize the rela 134 thus returning resistance 119 to the field circuit and causing the motor to again run at the intermediate speed. Similarly if the intermediate speed is below the mill capacity, the switch A will open deenergizing the relay 128 and returning the resistance 118 to the field circuit thus permitting the motor to again run at its full speed.

On the other hand, let us assume that after switches A and B have been closed and the motor reduced so its lowest speed, the rate of feed of the material is still too great for the mill capacity, the vacuum in the mill will be built up to a point suflicient to operate the third mercury switch C which will be actuated to break the circuit at contacts 58" and 57b thus deenergizing the coil 150 of the line contactor 149. This will drop the 'Contact plates 151 and 152, breaking the' motor armature circuit and bringing the motor to rest. At the same time, the bridge plate 153 will complete the circuit through the actuating coil 162 of the control relay 160 thus raising the bridge plate 163 and breaking the circuit through switch C and line contactor relay 149 at the contacts 158 and 159. This actuating circuit passes through the mercury switch A which still remains closed, and which will remain closed until after both switches C and B have been returned to their normal positions.

Since no material is being fed to the mill under these conditions, the mill will clear itself and the vacuum in the mill will be gradually reduced. The switch C will first reset itself, or be returned to normal position so as to close the circuit at contacts 58 and 571. However, since the coil 162 of control relay 160 is still energized, the circuit through switch C will remain open at this point and the line contractor relay 149 will not be energized. Consequently the mill must continue to clear itself until thc switches B and A have successivelyv been returned to their normal positions` and the normal low vacuum has been reestablished in the mill. vlien switch A returns to its normal position and the circuit is broken at contacts 57 and 58. thc control rclay 160 will be dcenergizcd permitting thisl rela)v to reset so that the starting circuit through switch C and the liuc contactor relay 149 may be reestablishcd. The motor will then be automatically re-started as first described.

If an overload occurs on the feeder, the circuit to the line contactor relay 150 is broken at contacts 155 and 156 thus stopping the motor, and the overload relay is prevented from resetting by the shunt coil 165, until the manual switch 116 has been opened. This action resets the overload relay and permits again closing switch 116 to restart the motor.

It will be understood that the control mechanism hereinabove described can befused to control the speed of devices other than the rotary feeder that has been described by way of example. The motor of a conveyor adapted to deliver material to any type of ap# paratus could be controlled in this manner.

I claim:

1. In a motor speed controller, a suction conduit and a pressure conduit each having a plurality of branches, a plurality of control units each comprising a switch, a suction device for operating the switch, a cut-off valve interposed between a branch of the suction pipe and the suction device, and an adjusta le pressure-operated controller connected with a branch of the pressure conduit and adapted to move the cut-off valve to open or closed positions at certain pressures predetermined by the adjustment of the controller.

2. In a motor speed controller, a suction conduit and a pressure conduit each having a plurality of branches, a plurality of control units each comprisingY a closed suction chamber, a ficxiblc diaphiagm forming one wall of the chamber, a pivotally' mounted mercury tube switch, means connecting the diaphragm with the switch for tilting the tube to make or break a circuit, a cut-off valve interposed between a branch of the suction conduit and the suction chamber, and an adjustable pressure operated controller connected with a branch of the pressure conduit and yadapted to move the cut-oli' valve at certain pressures predetermined by the adjustment of the controller.

3. In a motor speed controller, a switch, a suction operated device for opening or closing the switch, a suction conduit leading to the suction device, a cut-off valve in the suction conduit, and an adjustable pressure-operated controller for moving the eut-otl valve at pressures predetermined by the adjustment of the controller.

4. In a motor speed controller, a switch, a suction chamber. a flexible diaphragm forming one wall ot the chamber. means connected with the diaphragm for opening and closing the switch, a suction conduit leading to the suction chamber, a cut-otil valve in the conduit, a prcssuzc conduit. and an adjustable pressure operated controller connected with the pressure conduit and adapted to move the cut-oil1 valve to open or closed positions at certain pressures predetermined by the adjustment of the controller.

5. In a motor speed controller, a suction chamber, a flexible diaphragm forming one wall of the chamber, a suction conduit, a pivotally mounted mercury-tube switch, lever connections between the diaphragm and tube for tilting the switch to open or close a circuit, a cut-off valve interposed between the suction conduit and suctidn chamber, a pressure conduit and an adjustable pressure operated controller connected with the pressure conduit and adapted to move the cut-olf valve to open or closed positions at certain pressures predetermined by the adjustment of the controller.

6. In a motor speed controller, a closedcasing, a screened air inlet for the casing, a suction conduit having a plurality of branches projectin Y into the casing, and a plurality of contro units in the casing each unit comprising a switch, a suction device for operating the switch, and an adjustable pzessure-operated control valve interposed between the suction device and ,one branch of the suction conduit.

7. In a motor speed controller, a closed casing, a screened air inlet for the casing, a suction conduit and a pressure conduit each having a plurality of branches projecting into the casing, and a plurality of control units in the casing, each unit comprising a switch, a suction device for operating the switch, a cut-oft' valve interposed between one branch of the suction conduit and the suction device, and an adjustable pressure-operated controller connected with a. branch of the pressure conduit and adapted to move the cut-0H valve to open or closed positions at certain pressures predetermined by the adj ustmentof the controller.

8. In a motor speed controller, a closed casing, a screened air inlet for the casing, a suction conduit and a pressure conduit each having a. plurality of branches projecting into the casing, and a plurality of control units in the casing, each unit comprising a closed suction chamber, a flexible diaphragm forming one wall of the chamber, a pivotally mounted mercury-tube switch, means connecting the diaphragm with the switch for tilting the tube to make or break a circuit, a valve interposed between a branch of the suction con-duit and the suction chamber and adapted to alternatively place the suction device in communication with the source of suction or with atmospheric pressure, and an adjustable pressure operated controller connected with a branch of the pressure conduit and adapted to move the valve at certain pressures predetei'nlined by the adjustment of tbc controller.

9. The combination with a` pulverizing mill, exhaustingr means for withdrawing material from the mill in suspension in air,

a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor comprising a series of switches, a plurality of suction devices separately controlling the several switches, and means controlled b pressure variations in the mill for successively actuating the suction devices.

10. The combination with a pulverizing mill, exhaustin means for withdrawing material from tie mill in suspension in air, a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor comprising a series of switches, and means controlled by ressure chan es in the mill for successive y actuatin t e switches.

11. The com ination with a pulverizing mill, exhausting means for withdrawing material from the mill in suspension in air, a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor comprising a series of switches, and pneumatcall controlled means responsive to pressure c anges in the mill for successively actuating the switches.

12. The combination with a pulverizing mill, exhausting means for withdrawing material from the mill in suspension in air, a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor comprising a series of switches, a suction motor for opening and closing each switch, a suction conduit leading from the mill to each of the suction motors, and an adjustable ressure-controlled valve in each suction con uit.

13. The combination with a pulverizing mill, exhausting means for withdrawing material from the mill in suspension in air, a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor com rising a series of switches, a suction motor or opening and closing each switch, a suction conduit leading from the mill and having a branch communicating with each suction motor, an adjustable pressure controlled valve in each branch of the suction conduit, and a pressure conduit leading from the mill, said latter conduit having branches leading to the several valves.

14. The combination with a pulverizing mill, exhausting means for withdrawing material from the mill in suspension in air, a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor comprising a series of switches, and means for separately and automatically opening and closing the several switches in response to pressure changes in the mill comprisinga closed suction chamber for each switch, a flexible diaphragm forming one wall of the chamber,

means actuated by the diaphragm for opening and closing the switch, a suction conduit leading from the mill and having a branch leading to each suction chamber a valve in each branch conduit adapted to alternatively place the suction device in communication with the mill or with atmospheric pressure, an adjustable pressure actuated means for operatin this valve, and a ressure conduit leading rom the mlll and aving a branch leadiny to each pressure actuated means.

15. he combination with a pulverizing mill, exhausting means for withdrawing material from the mill in suspension in air, a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor comprising a plurality of control circuits, a plurality of switches in said circuits, a plurality of suction devices separately controllin the several switches, and means controlle by pressure variations in the mill for successively actuating the suction devices.

16. The combination with a pulverizing mill, exhausting means for withdrawing material from the mill in suspension in air, a feeder for the mill, and a variable speed motor for driving the feeder, of means for controlling the speed of the motor comprising a plurality of control circuits, a plurality of switches in said circuits, and means for se arately and automatically opening and closing the several switches in response to pressure variations in the mill comprising a closed suction chamber for each switch, a flexible diaphragm forming one wall of the chamber, means actuated by the diaphragm for opening and closing the switch, a suction conduit leading from the mill and having a branch leading to each suction chamber, a valve in each branch conduit adapted to alternatively place the suction device in communication with the mill or with atmospheric pressure, an adjustable pressure actuated means for operatin this valve, and a pressure conduit leading from the mill and having a branch leading to each pressure actuated means.

PHILIP DAVIDSON. JOE CRITES. 

